In dual y-axis charts, showPZeroPlaneValue attribute of the chart object is used to show/hide the zero plane value for the primary y-axis and showSZeroPlaneValue is used to show/hide the zero plane value for the secondary y-axis.

Showing/hiding the zero plane

Zero plane can be removed in the line, scatter and bubble charts but not in the column and area charts because they use it as their base to draw. A scatter chart with the vertical zero plane hidden is shown below: